Archive for Low Impact Design

Here are some things to weigh when considering rainbarrels as part of a stormwater BMP. While rain-harvesting and storage are nice potential side benefits of the barrel, its future success relies on keeping the focus squarely on stormwater capture. If you look around the internet and review municipal rainbarrel programs that are being promoted, they are often discussing the 50- to 60-gallon barrel like it is a viable option.

It simply isn’t. Consisder these conservative assumptions:

Let’s say a typical residential roof is 1200 square feet (it is closer to 1600). And, let’s say that a minor storm passes through – on the order of 1/4″. That would create a runoff volume of approximately 187 gallons. Let’s assume that only 60 percent of that runoff made it to the downspout due to ponding and poor pitching of the roof. That would result in a runoff to the downspouts of approximately 112 gallons. If the homeowner had 2 downspouts and 2 50-gallon barrels, the system is are already overflowing. With 4 downspouts and 4 barrels, the system is more than half full after a very small storm – just one storm. Furthermore, the overflow checks that are typically designed into a rainbarrel are not able to discharge at a rate that can keep up with the runoff rate into the barrel. So, the notion that the barrel is safe from overflowing during a storm is on shaky ground.

Here comes the next issue. The homeowner wants to be able to store this rainwater for future use, but the weather is a little rainy and the need to irrigate is not currently there. A couple of days later, the next small storm comes through and your barrels that should be empty are starting off at 56 percent of capacity. The new 1/4″ storm overflows the barrels. And, this is if 4 barrels are installed – not typically the case.

Where does that leave us? If rainbarrels are to be considered as a viable BMP, then larger ones need to be used. Successful programs like those used in the cities of Pittsburgh and Washington, D.C., use barrels with 3 times the typical volume capacity at 150-gallons. This could provide some storage capacity for future use in more arid regions of the country. In the areas prone to heavier rainfall, use of a couple of larger barrels offers the ability to capture runoff from more substantial events, but still not likely act as a harvesting tool.

The long and short of it is this. Focus should primarily be on stormwater capture, especially of that first flush. Once that water is captured, it will likely need to be emptied onsite through controlled overflow to a drywell or dedicated infiltration area on the property. Homeowners need to be educated on these issues and keep tabs on capacity and maintenance.

A final point should be considered when designing rainbarrels for storwater capture. Is it properly constructed? I run across a lot of make-your-own barrel websites that are not always considering issues such as proper overflowing or covering of the barrel. The last thing a homeowner wants to deal with is a massive buildup of water right next to the foundation, or a mosquito population explosion in the sideyard.

While the DIY approach has some appeal, by and large the focus should be on proper design and engineering. If we can get away from poor planning and design, rainbarrels can be a great addition to the lot-level approach of managing stormwater.

One of the questions that comes up quite often in the research about Low Impact Development is how to implement the design when you have naturally low infiltrating conditions (i.e. low permeable soils or shallow groundwater/bedrock). In design scenarios like these you are inevitably going to be faced with major drainage issues, ponding, and vector control problems. Using the State of California as an example, ponding present after 4 days is going to be the limiting factor on your BMP design.

Daniel Apt of RBF consultants presented a nice discussion on this very subject in 2008. Mr. Apt summarized the measures to help reduce runoff from these sites as follows:

Reduce/Minimize Total Impervious Areas

Minimize Directly Connected Impervious Areas

Limit use of sidewalks

Reduce road/driveway length and width

Modify/Increase Drainage Flow Paths

Maximize overland sheet flow

Conserve natural areas

Minimize disturbance

Preserve infiltratable soils

Preserve natural depression areas

Preserve vegetation

The presentation goes into the benefits of using measures such as green roofs, rain barrels, cisterns, bioretention strips, and grassed swales as possible ways to working around infiltration issues on a site, while still drastically reducing offsite runoff.

One of the trends that I have been spotting in research studies of LID acceptance into practice has been this concept of “proof of benefit”. Essentially, the idea is that by having high-profile, high-traffic demonstration projects, stakeholders will see the benefit and will encourage LID’s spread through new development, as well as through retrofits in urban settings. It’s a great concept, but one that takes a decade to truly take hold in a municipality.

The idea behind this website has been pretty simple. Take a look at the tools that are available in stormwater BMP design and point out the more novel approaches and interesting research being done in sustainable stormwater engineering. To help further the development of “proof of benefit” as a way of spreading Low Impact Development in communities, I am proposing the development of an LID project database. It is possible this has been done to a certain extent. I claim no mantle of originality to any ideas presented on this site and this is certainly no different. Simply, what I would like to see is a much more comprehensive look at projects that have been completed, are currently in progress, or are in their infancy. This will be a laborious process – one that will certainly require input and collaboration. To this end, I make my formal request to others right now.

The idea is this. Send me information on any project that is available in the public domain. In particular, I need to be able to start with the basics such as: project location (street address), general description of the project, type of LID approach being used, status of the project, and if possible, a project contact. I will most likely expand the database to include other fields as development progresses, but starting off simple will get me to a finished product more quickly. Ideally, I would like to see this be a living databse that is fed by users as new projects spread through North America.

In addition to serving as a way of finding demonstration projects, I envision a database that is tracking the popularity of different LID approaches and spotting trends in technology – perhaps even helping to shine a light as to where LID is falling behind in acceptance.

In 2008, a research study was sponsored by the State of Washington to survey the progress being made by 19 local governments in adopting LID controls into their building codes. A representative from each of the 19 municipalities was asked the same set of questions regarding the barriers seen to LID implementation. Some of the trends they found in the responses include the following:

Perception that LID is not a proven technology

General public and government officials lack understanding of LID

Perception that LID is more expensive when compared to traditional BMPs

Planning departments lack training to review and inspect LID controls

Developers lack knowledge of LID

LID difficult to use in urban settings, difficult to retrofit

One of the more interesting solutions to the obstacles focused on funding of “high traffic” demonstration projects to help provide a local proof of benefit.

The issue of quantifying reduction rates can be a difficult one due to the different capacities of tree species. For more information on use of trees as a stormwater BMP, please refer to the recent study on Trees and Structural Soils by the Department of Urban Forestry at Virginia Tech University. Developers and design professionals can also refer to the Green Values Calculator, which allows you to create hypothetical designs using trees and other green interventions and quantifies the results in terms of costs savings and reduction in stormwater discharge.

Over the next several weeks, I will be presenting a series on how the municipalities of Pine Lake, Sacramento, Portland, and Indianapolis each went about changing the local building code to include stormwater credits for trees.

Understanding who the stakeholders are is quite simply the most important part of the sustainable stormwater discussion. One of the more impactful and concise tools in my search for useful storwater resources is called The Language of Change. Essentially, this brief document helps you frame the green stormwater argument in terms that each of your stakeholders can understand. By choosing your words properly, you improve the chances of connecting with your audience.

Starting with the notion that community stakeholders tend to view stormwater as “dirty”, “a nuisance”, or “threatening”, the document touches on using “rainwater” as a synonym. Stormwater is typically viewed as something to be diverted and hidden away in its pipe until reaching an unseen destination. When the traditional system of handling it is overloaded, then its nuisance or threating side comes out in the form of flooding. Rainwater, however, is viewed as something that can be collected, spread out, harvested, and reused. A simple change in wording, can transform the idea from waste product into valuable and renewable resource.

Getting buy-in from the different stakeholders is critical to the process. Regulators are going to respond more keenly to traditional terms like “TMDLs”, Park & Recreation Districts to “open space”, and engineers like myself will be wooed by “infiltration”. Choosing your words carefully, helps to make the case to each member of your audience.

The document is part of a much larger set of tools organized by the Water Environment Research Foundation at its sustaiable stormwater BMPs website Using Rainwater to Grow Livable Communities. There you can find resouces dedicated to each of the stakeholders, as well as case studies, and a comprehensive toolbox.

The most recent edition of the journal Stormwater included an article on urban retrofitting. The article focused its attention on 3 retrofit projects in Portland, Minnesota, and Seattle. In particular, the article zeroes in on how each project managed the challenge of incorporating the retrofits with limited space.

Portland

In the case of the Portland project, a parking garage was redesigned to reroute stormwater to infiltration planters along two sides of the structure. The major challenge was redesigning the plumbing to properly redirect the stormwater to planters. Narrow infiltration planters were constructed with permebale soil mix and native plants to help treat and infiltrate the runoff. The planters are able to infiltrate a minimum of 2 inches of rainwater per hour and can handle practically all of the stormwater from a 2-year storm event.

Minnesota

By taking a street in the town of Burnesville, narrow strips in front of residential properties were carved out, sometimes using retaining walls, to cluster together a series of rain gardens. Getting buy-in from the the residents was the biggest challenge, but an educational outreach program was developed and helped to achieve 80% participation rates. Sidewalk cut-outs were incorporated to help direct street runoff to the raingardens, which were able to accomodate 0.9 inches of runoff from the tributary hardscape. There hasn’t been any concern with vector control issues, as gardens have typically dried in a 3-4 hour period. When compared with a similar nearby street also feeding Crystal Lake, runoff volumes have been reduced by 90 percent.

Seattle

On a much grander scale, the city of Seattle took on a retrofit project incorporating 32 acres and 15 residential blocks. Working with the existing topography and regrading portions of streets to create a more meandering path through the neighborhoods, the engineers were able to divert stormwater to culverts, catch basins, vegetated swales, raingardens, and cascades. Swales were used in steeper areas to help control runoff velocity and volumes, while raingardens were a common feature in flatter terrain. As with the Minnesota raingarden clutstering, this large project involved networks of stormwater BMP features that worked to slow runoff, treat it, and infiltrate it to help recharge the groundwater tables.

Challenges

The article touches on several of the challenges to projects like these. Limited space can be one of the largest obstacles and requires a great deal of coordination with project scheduling to prevent disruption to business and residences. It obviously impacts the design and overall effectiveness of the project and requires creative solutions to address proper stormwater management.

One of the other important considerations is educational outreach efforts. Business and homeowners often need to be educated on the need to promote infiltration. Allowing for buy-in keeps the project strong and growing. Homeowners are a critical part of the maintenance to residential BMPs, while business owners can get LEED credits and can promote their reputation as green businesses.

The biggest challenge is funding. The three examples cited in the Stormwater article all had significant funding from city grant programs. These projects require large inflows of funds to carry through all the design objectives. However, more successful projects cropping up like these examples can make it easier in the future for public works agencies to seek the necessary funds to promote urban retrofits on a larger scale.